Films of polymeric linear polyesters have excellent draw orientation and have proved especially well suited for biaxial film orientation. These polymeric films, especially those of polyethylene terephthalate or PET, are strong and have excellent inherent chemical and thermal properties. In addition, they have good optical clarity, toughness, and static properties, which makes them extremely suitable for use as substrates for ink jet printing. For this application, the film can be transparent, or it can be pigmented with, for example, barium sulfate to have a high gloss.
For ink jet printing the film is coated with an ink receptive coating. As described, for example, in Atherton, European Patent Publication 698,502, the ink receptive coating typically comprises a cellulose derivative, such as hydroxyethyl cellulose or methyl cellulose. Other water soluble components, such as poly(vinyl alcohol), poly(vinyl pyrrolidone), and poly(ethylene oxide) may also be present in the ink receptive coating. However, unprimed polyester film is not very receptive to coating with hydrophilic materials. Adhesion between the hydrophobic unprimed polyester film and the hydrophilic ink receptive is poor.
The polyester film is pretreated to improve its adhesion to the ink receptive coating. An underlayer that improves the adhesion of the film to the ink receptive coating is coated onto the film. Pretreatments that improve the adhesion of polyester films to solvent-based coatings have been disclosed in, for example, Pears, U.S. Pat. Nos. 4,244,270, and 4,391,767. However, these pretreatments are not effective for water-based coatings. Thus, a need exists for a pretreatment that will improve the adhesion of polyester films to water-based coatings.